The long-term objectives of this project are to elucidate the molecular basis of plant innate immunity in response to bacterial pathogens. In this application, experiments will be carried out to elucidate the molecular basis of bacterial pathogen recognition by the NLR class of innate immune receptors in Arabidopsis thaliana. A major aim of these studies is the identification and characterization of the downstream signaling events that result from the activation of NLR proteins. The NLR protein family of immune receptors was originally described in plants as the major class of disease resistance (R) proteins that control disease resistance in plants. Subsequently, it was discovered that this class of protein also functions in animals as innate immune receptors as more than twenty have been described to date. Our research will focus on the role of the NDR1 and RIN4 proteins in both PAMP and effector-triggered immunity. Our recent results have revealed that NDR1 protein compromises both flg22-induced innate immunity and the RPS2 signal transduction pathway. Interestingly, the NDR1 shares protein folds and a predicted 3-D structure with the LEA14 protein that has been shown to be involved in abiotic stress responses. The predicted 3-D structure of NDR1 will allow us to perform a structure and function analysis by mutating amino acids that are predicted to be involved function and will allow us to ascertain the role NDR1 plays in immune receptor location and signal transduction. Furthermore, we propose to study the molecular events associated with the negative regulation of the RPS2 protein by the Arabidopsis RIN4 protein and the subsequent activation the AvrRpt2 effector protein. Once the RPS2 protein is activated, this application will identify and characterize the direct targets of the activated RPS2 protein by employing next-generation Illumina sequencing technologies in conjunction with a comprehensive yeast-one hybrid library that represents all the transcription factors known to date in Arabidopsis. To accomplish these goals, experimental approaches will be designed to employ a combination of biochemical, genetic, cellular, proteomic and functional genomic approaches to characterize the signal transduction events controlling the expression of disease resistance in this model pathosystem.